In order to maximize the usage of the vehicles or rolling stock of various transportation systems, it has been found to be highly advantageous to automatically derive the identity and other necessary information from a moving train, mass transit car or bus as it passes a wayside point along its route of travel. It will be appreciated that an automatic vehicle identification system finds particular utility in railroad and mass and/or rapid transit operations. For example such a system has been employed in identifying the cars of a moving train entering a classification yard, a station or a switching conjunction or any other location along its route of travel. Similarly, such an automatic identification system may be utilized to obtain certain information from mass transit vehicles to establish and verify the times of arrival at stations or stopping points as well as to monitor the positions of the vehicles along this route of travel.
While the prior art discloses a number of arrangements for automatically identifying moving vehicles, these previous systems have suffered from one or more shortcomings, such as, being unreliable in operation due to climatic condition being expensive to maintain due to environmental adversities or being unacceptable due to inability to conform with certain requirements. In one previous system, it is proposed that each moving vehicle be equipped with one or more color coded label members which would be scanned by a source of white light so that reflected radiant energy would be directed back to a wayside scanning apparatus. The received reflected radiant energy is divided into two separate color paths for processing, decoding and providing signals which identify the particular vehicle carrying the coded label. The vehicle-carried labels include a plurality of reflective or non-reflective markings which are carried by a suitable backing member. The backing member is suitably attached to the side or sides of the given vehicle. In practice it has been found that the spectral response characteristics of the coded markings are greatly impaired by climatic and environmental conditions to the point where little if any intelligible information is received by the wayside scanner. That is, the build-up of dirt, grease, tar, oil, dust and other foreign matter covers and obliterates the coded markings so that the coded identity is unreadable unless the labels are frequently cleaned and reconditioned. Similarly the emitted rays of white light cannot effectively penetrate fog and mist and are blocked and dispersed by snow flakes and rain drops so that unacceptable and unsatisfactory readings occur during adverse climatic conditions. Another problem in reliable reading of the coded markings arises when the car-carried labels are skewed or tilted by uneven loading, swaying and vibrational movement which occurs as the moving vehicle passes a wayside scanner. Thus, it will be appreciated that the above noted vehicle identification system is expensive to maintain as well as unreliable in operation due to the outdoor milieu in which it is required to function:
In another prior art arrangement, it is suggested that a depending portion of a railway vehicle, such as, the truck or the like, be magnetized with a preselected polarity pattern to form the coded identity which is unique to the particular vehicle. Such a magnetic identification system is impractical for several reasons. First, it will be appreciated that railway vehicles are exposed to severe shock and vibration and experience continuous pounding which causes the alignment of dipoles in the cast iron trucks thereby creating magnetic regions having a much stronger intensity than that of the coded magnetic area. Hence, the significance of the magnetic code was destroyed or obliterated which has little, if any, relationship with the identity of the vehicle. Second, it is necessary to mount a magnetic reading head extremely, if not, illegally close to the track rail in order to detect the magnetic coded regions. Thus, the wayside reading device would not have the required clearance with the vehicle so that the system could not be approved and accepted by the railroad industry.
Yet another prior art system employs an electromagnetic scheme having a vehicle-carried transponder and a wayside stationed interrogator. The transponder includes passive elements which are inductively activated as they pass an interrogating station. Hence, the transponder provides a uniquely coded response signal when interrogated by an interrogating station which is thereafter decoded by the interrogation station to establish the desired input data relating to the characteristics of the particular moving vehicle upon which the transponder is mounted. It will be appreciated that passive responsive elements require precise physical alignment and are adversely influenced by a variety of environmental factors which affect the reliability and accuracy of the system. In addition, extraneous noise signals have an adverse effect on prior types of transponder-interrogator systems and result in the development of inaccuracies in the coded information transmitted by the transponder and received at the interrogating station.
Accordingly, it is an object of this invention to provide a new and improved transponder for an automatic vehicle identification system.
A further object of this invention is to provide an automatic vehicle identification system having a unique batteryless carborne transponder energized by an interrogating signal to produce coded signals peculiar to the particular vehicle.
Another object of this invention is to provide an improved transponder for generating a phase modulated coded signal for identifying a given object as it passes an interrogating area.
Still a further object of this invention is to provide a novel inert receiver-transmitter circuit arrangement responsive to an interrogating signal for providing d.c. operating potential for energizing the receiver-transmitter whereby coded information is transmitted so long as the receiver-transmitter is under the influence of the interrogating signal.
Still another object of this invention is to provide a unique inductively powered type of transponder for transmitting a phase modulated message upon the reception of an interrogating signal.
Yet a further object of this invention is to provide a novel transponder having a pick-up coil supplying a rectifier network to produce d.c. operating power, a frequency divider, a shift register, a latching network, a logic network, and an amplifier fed transmitting coil for propagating a coded message upon the reception of an interrogating signal.
Yet another object of this invention is to provide a new and improved phase modulation transponder which is economical in cost, simple in design, reliable in operation, durable in service and efficient in operation.